The New Hampshire Fish and Game Department is warning that some lakes and ponds that traditionally have been safe for ice fishing and other outdoor recreation are not safe this year.

Officials are advising people to use extreme caution and check the ice thickness for themselves before going onto any frozen body of water. Participants in this weekend's fishing derby have been warned to avoid shorelines and inlets where ice can be particularly dangerous.

The department says warm temperatures and high winds have affected ice formation, particularly on the state's bigger lakes.

Officials say aerial photographs show ice conditions on some parts of Lake Winnipesaukee are unsafe, including an area of open water near Welch Island.

Fish and Game Lt. James Goss says people are advised not to drive vehicles onto the ice because of the unpredictable conditions.